1. FIELD OF THE INVENTION
This invention is concerned with the production of synthetic fibers. It is particularly concerned with that step in fiber production wherein a plurality of tow bands of drawn continuous filaments are guided to form a composite bundle array suitable for crimping in a stuffer box crimper.
2. DESCRIPTION OF THE RELATED ART
Various types of equipment have been used to converge and shape tow of fibers for stuffer box crimping. However, as production methods change and different products are processed on the same equipment, the apparatus used in production must be changed or adjusted. These changes are normally done manually by operators at the beginning of production runs and seldom are checked throughout the run. Typically the operators make visual checks of the crimp uniformity tow shape and edge position to determine the appropriate adjustments for the guides.
There is a problem with visual checks and edge measurements in that they do not account for variations in tow thickness between the edges, i.e. uneven tow mass distribution which results in non-uniform crimp.
Most synthetic staple fibers are given an appreciable amount of crimp to facilitate their conversion into spun yarn and, in the case of carpet fibers, to improve bulk and coverage to enhance apparent value of the final product. Most commonly, this crimp is established by passing a plurality of tow bands of drawn continuous filaments through a "stuffer box" type crimper as disclosed by U.S. Pat. No. 2,311,174 to Hitt. In that crimper device the bundle of continuous filaments is led into the nip of two rolls and forced into a restricting chamber against a movable gate.
Pressure applied to the gate by an air cylinder or spring causes the bundle to fold back upon itself and crimp is formed. The back pressure applied to the gate, the nip roll pressure, speed and denier loading of the crimper establish the crimp level and geometry (frequency and amplitude) of the crimp. The Hitt crimping device and most commercially available crimpers can handle relatively wide variations in bundle thickness uniformity. This can result in the crimpers producing a wide variation in across-the-band crimp variability without detection or upset. Since crimp loading on most commercial crimpers can be varied across a broad range of from 50,000 to 400,000 denier per inch of roll loading, considerable variability in tow geometry and crimp level can occur, especially at high denier loading without process upset or visual observation of change. If the tow band fed to the crimper is not uniform, it will not be evenly squeezed between the feed rolls of the crimper which results in non-uniform crimp both across and along the tow band. In extreme cases fiber damage can also occur from localized slippage or abrasion. Thick sections are gripped more positively and crimping force is more effectively transmitted to these sections resulting in higher crimp. Conversely, thinner sections transmit load less effectively which results in low crimp regions. After crimping, the tow should also have the crimped fibers uniformly intermeshed so the bundles hold together without splitting which impacts on downstream process uniformity such as cut length. Hence, the distribution of the tow fibers or filaments preparatory to crimping is an important step in the conversion process and it must be controlled to achieve good crimp uniformity.
When dynamic changes occur, they must be detected and immediate corrective action taken if product uniformity is to be controlled within the tight limits demanded for quality spun products. To achieve high quality in crimp uniformity, tow entering a crimper must be shaped and formed to provide as uniform a cross section as possible.
The prior art utilized any number of devices such as stacking bars or rolls, curved bars or rolls, and edge sensing and automatic centering devices to accomplish the guiding task. These devices used alone or in combination, are normally set at the beginning of production runs based on visual inspection or limited crimp measurements of the tow by the operator and changes are seldom attempted unless a process upset occurs. Where automatic operation was attempted, it was limited to centering the edges of the tow and controlling its width with no concern for the actual tow cross-section characteristics or alignment required for across band crimp uniformity.